In the manufacturing of a semiconductor integrated circuit such as IC or LSI, a substrate such as a semiconductor wafer is generally subjected to various heat treatments, including film forming processing, oxidation/diffusion, etching, annealing, the formation of a silicon oxide film, sintering, etc. A vertical batch-type heat treatment apparatus is used to process a plurality of substrates at a time, as described in patent documents 1 to 4.
In an exemplary heat treatment apparatus, a wafer boat loaded with a plurality of, e.g. about 100 to 150, substrates (semiconductor wafers) is raised by means of a lifting elevator mechanism to load (insert) the wafer boat into a vertical quartz processing container from a loading chamber having an inert gas atmosphere, disposed below the processing container. Thereafter, the bottom opening of the processing container is hermetically closed by a cap having an O-ring, and heat treatment, such as film forming processing, is carried out in the hermetically-closed processing container. After the heat treatment, the wafer boat is unloaded (lowered), and transfer of substrates is performed to replace the processed substrates in the wafer boat with unprocessed substrates. The same heat treatment is then repeated.
A boat elevator, provided in the loading chamber, may be used to vertically move the wafer boat. The transfer of substrates may be performed by means of a transfer mechanism provided in the loading chamber.
<Prior Art Documents>
Patent document 1: Japanese Patent Laid-Open Publication No. H02-130925
Patent document 2: Japanese Patent Laid-Open Publication No. H06-224143
Patent document 3: Japanese Patent Laid-Open Publication No. 2001-093851
Patent document 4: Japanese Patent Laid-Open Publication No. 2007-027772
As described above, the bottom opening of the processing container is hermetically closed by the cap during heat treatment. Further, in order to enhance the sealing performance, the lifting elevator mechanism continually presses on the cap with a predetermined force during heat treatment.
On the lifting elevator mechanism are applied both the load of the wafer boat containing substrates and the load of the internal pressure acting on the cap. The load of the internal pressure is considerably large during a heat treatment, such as sintering, which is carried out at a processing pressure higher than atmospheric pressure. Thus, such a heat treatment necessitates a lifting elevator mechanism having a reinforced structure and a powerful drive motor, leading to an increased apparatus cost.
To increase the efficiency of production of semiconductor integrated circuits, substrates are expected to have a larger diameter. For example, there is a demand for increasing a substrate diameter from 300 mm to 450 mm. The load of a wafer boat, holding 150 such large-diameter substrates, will be about 400 kg. In addition, the increase in substrate diameter requires an increase in the area of a cap for closing the opening of a processing container. When performing a heat treatment at a processing pressure higher than atmospheric pressure, the increase in the area of the cap leads to an increase in the load of internal pressure. This necessitates the use of a lifting elevator mechanism having a reinforced structure, resulting in an increased cost.